There are three major digital video standards, Apple's Quicktime, Microsoft's Video for Windows, and the MPEG families. MPEG-1 promises to be accepted as a cross platform solution for handling video.
Both Quicktime and Video for Windows allow varied frame rates, but with the disadvantage of large file sizes despite data compression, and relatively poor picture quality and poor audio/picture synchronization. MPEG has smaller file sizes and better image quality but at a frame rate fixed between 24 and 30 frames per second (fps). A frame of video data contains the data necessary to display a full screen view of the one (still) picture which together with the other frames when played sequentially forms a moving picture.
Both Quicktime and Video for Windows store a data compressed video image (but still quite large) and linked audio file. Both the video and the audio portions are time stamped within the files, but this, by its nature, includes slight inaccuracies and the audio and the video may not be completely synchronized.
MPEG-1 was developed by the Motion Picture Experts Group, a consortium of Multimedia companies, to maximize an efficient platform for an independent video solution. MPEG-1 is a comparative frame compression system wherein once every 5th to 15th frame an actual image (I) frame exists. Between the I frames are bi-directional (B) and predictive (P) frames. The B frame contains the differences between the frame before the B frame and after the B frame. An P frame has an algorithm that a computer uses to approximate the frame. Two multiple sequences are typically used in the art: (i) a sequence of I BBBP BBBP BBBP (repeated), and (ii) I BBP BBP BBP BBP BBP (repeated). Since most of the frames contain only partial image information and there is actually little change between frames, the file sizes are much smaller than in Quicktime and Video for Windows. The audio in MPEG-1 is broken up into individual segments as well. There are the same number of audio packets as there are video frames. This allows the decoder to know which audio packet to play with each video frame thereby allowing an improved synchronization of audio to video over Quicktime and Video for Windows.
MPEG-1 was designed for frame rates of 24, 30 and higher. One limitation of MPEG-1 is that special hardware must be used to playback the audio and video files at full speed and performance. This special hardware, is expensive. When MPEG-1 is played in a personal computer (PC), without the special hardware many frames are skipped causing a jerky playback. There is a need to provide varied frame rate playback using existing distribution channels and playback solution. Creating an MPEG-1 at 15 fps approximately halves the size of the files without significant reduction in playback quality for existing systems without the aforementioned special hardware.
Many or most users on the internet have relatively slow modem connections to the internet, and therefore these systems are slow in downloading almost any significantly sized file. Also, real-time audio/video playing while downloading requires lower data and frame rates due to the existing telecommunications equipment available to most users on the internet. The games market using Quicktime or Video for Windows requires 3 or 4 CD-ROM disks, MPEG-1 will reduce this to 1 or 2 disks. These factors suggest that there is a limitation of the present systems and a need for a lower frame rate video with accurately synchronized audio.
However, if a video source is captured and digitized at 15 fps and the audio is simultaneously captured and digitized at the standard sampling rates of from 11.025 kHz to 44.1 kHz, then combining the video and audio files in the normal MPEG-1 multiplexing will create a problem. MPEG-1 encoding software assumes that the frame rates are 30 fps. So if there are 150 frames of video data taken at 15 fps, or ten seconds worth of video, the software looks for 5 seconds worth of audio to combine with the 150 frames. Obviously no matter how played the multiplexed files will not play properly for there is actually ten seconds of video and five seconds (the first five seconds) of matching audio. This limitation is the subject of the present invention.
It is an object of the present invention to provide apparatus and method to record a video and associated synchronized audio via a varied frame rate technique, and where playback utilizes standard software and hardware, where said standard hardware and software operates at a fixed frame rate that is different from the particular (variable) frame rate of the recording, such that the resulting video and audio are synchronized.
It is an object of the present invention to provide a varied frame rate with MPEG-1 picture quality and synchronized audio.
Yet another object of the present invention is to provide a lower frame rate video with accurately synchronized audio.
It is another object of the present invention to provide a smaller audio portion and/or video portion of the file.